"IO" -> "System".

Get rid of the separate opt-in IO class and replace it with a core
System class.

- Remove wren_io.c, wren_io.h, and io.wren.
- Remove the flags that disable it.
- Remove the overloads for print() with different arity. (It was an
  experiment, but I don't think it's that useful.)
- Remove IO.read(). That will reappear using libuv in the CLI at some
  point.
- Remove IO.time. Doesn't seem to have been used.
- Update all of the tests, docs, etc.

I'm sorry for all the breakage this causes, but I think "System" is a
better name for this class (it makes it natural to add things like
"System.gc()") and frees up "IO" for referring to the CLI's IO module.

test/core/bool/equality.wren

@@ -1,23 +1,23 @@
-IO.print(true == true)    // expect: true
-IO.print(true == false)   // expect: false
-IO.print(false == true)   // expect: false
-IO.print(false == false)  // expect: true
+System.print(true == true)    // expect: true
+System.print(true == false)   // expect: false
+System.print(false == true)   // expect: false
+System.print(false == false)  // expect: true
 
 // Not equal to other types.
-IO.print(true == 1)        // expect: false
-IO.print(false == 0)       // expect: false
-IO.print(true == "true")   // expect: false
-IO.print(false == "false") // expect: false
-IO.print(false == "")      // expect: false
+System.print(true == 1)        // expect: false
+System.print(false == 0)       // expect: false
+System.print(true == "true")   // expect: false
+System.print(false == "false") // expect: false
+System.print(false == "")      // expect: false
 
-IO.print(true != true)    // expect: false
-IO.print(true != false)   // expect: true
-IO.print(false != true)   // expect: true
-IO.print(false != false)  // expect: false
+System.print(true != true)    // expect: false
+System.print(true != false)   // expect: true
+System.print(false != true)   // expect: true
+System.print(false != false)  // expect: false
 
 // Not equal to other types.
-IO.print(true != 1)        // expect: true
-IO.print(false != 0)       // expect: true
-IO.print(true != "true")   // expect: true
-IO.print(false != "false") // expect: true
-IO.print(false != "")      // expect: true
+System.print(true != 1)        // expect: true
+System.print(false != 0)       // expect: true
+System.print(true != "true")   // expect: true
+System.print(false != "false") // expect: true
+System.print(false != "")      // expect: true

test/core/bool/not.wren

@@ -1,3 +1,3 @@
-IO.print(!true)    // expect: false
-IO.print(!false)   // expect: true
-IO.print(!!true)   // expect: true
+System.print(!true)    // expect: false
+System.print(!false)   // expect: true
+System.print(!!true)   // expect: true

test/core/bool/to_string.wren

@@ -1,2 +1,2 @@
-IO.print(true.toString)  // expect: true
-IO.print(false.toString) // expect: false
+System.print(true.toString)  // expect: true
+System.print(false.toString) // expect: false

test/core/bool/type.wren

@@ -1,4 +1,4 @@
-IO.print(true is Bool)      // expect: true
-IO.print(true is Object)    // expect: true
-IO.print(true is Num)       // expect: false
-IO.print(true.type == Bool) // expect: true
+System.print(true is Bool)      // expect: true
+System.print(true is Object)    // expect: true
+System.print(true is Num)       // expect: false
+System.print(true.type == Bool) // expect: true

test/core/class/equality.wren

@@ -1,13 +1,13 @@
-IO.print(Num == Num)  // expect: true
-IO.print(Num == Bool) // expect: false
+System.print(Num == Num)  // expect: true
+System.print(Num == Bool) // expect: false
 
 // Not equal to other types.
-IO.print(Num == 123)  // expect: false
-IO.print(Num == true) // expect: false
+System.print(Num == 123)  // expect: false
+System.print(Num == true) // expect: false
 
-IO.print(Num != Num)  // expect: false
-IO.print(Num != Bool) // expect: true
+System.print(Num != Num)  // expect: false
+System.print(Num != Bool) // expect: true
 
 // Not equal to other types.
-IO.print(Num != 123)  // expect: true
-IO.print(Num != true) // expect: true
+System.print(Num != 123)  // expect: true
+System.print(Num != true) // expect: true

test/core/class/name.wren

@@ -1,13 +1,13 @@
 class Foo {}
 
-IO.print(Foo.name) // expect: Foo
-IO.print(Foo.type.name) // expect: Foo metaclass
+System.print(Foo.name) // expect: Foo
+System.print(Foo.type.name) // expect: Foo metaclass
 
 // Make sure the built-in classes have proper names too.
-IO.print(Object.name) // expect: Object
-IO.print(Bool.name) // expect: Bool
-IO.print(Class.name) // expect: Class
+System.print(Object.name) // expect: Object
+System.print(Bool.name) // expect: Bool
+System.print(Class.name) // expect: Class
 
 // And metaclass names.
-IO.print(Object.type.name) // expect: Object metaclass
-IO.print(Bool.type.name) // expect: Bool metaclass
+System.print(Object.type.name) // expect: Object metaclass
+System.print(Bool.type.name) // expect: Bool metaclass

test/core/class/supertype.wren

@@ -5,11 +5,11 @@ class Bar is Foo {}
 class Baz is Bar {}
 
 // A class with no explicit superclass inherits Object.
-IO.print(Foo.supertype == Object) // expect: true
+System.print(Foo.supertype == Object) // expect: true
 
 // Otherwise, it's the superclass.
-IO.print(Bar.supertype == Foo) // expect: true
-IO.print(Baz.supertype == Bar) // expect: true
+System.print(Bar.supertype == Foo) // expect: true
+System.print(Baz.supertype == Bar) // expect: true
 
 // Object has no supertype.
-IO.print(Object.supertype) // expect: null
+System.print(Object.supertype) // expect: null

test/core/class/type.wren

@@ -1,15 +1,15 @@
 class Foo {}
 
 // A class is a class.
-IO.print(Foo is Class) // expect: true
+System.print(Foo is Class) // expect: true
 
 // Its metatype is also a class.
-IO.print(Foo.type is Class) // expect: true
+System.print(Foo.type is Class) // expect: true
 
 // The metatype's metatype is Class.
-IO.print(Foo.type.type == Class) // expect: true
+System.print(Foo.type.type == Class) // expect: true
 
 // And Class's metatype circles back onto itself.
-IO.print(Foo.type.type.type == Class) // expect: true
-IO.print(Foo.type.type.type.type == Class) // expect: true
-IO.print(Foo.type.type.type.type.type == Class) // expect: true
+System.print(Foo.type.type.type == Class) // expect: true
+System.print(Foo.type.type.type.type == Class) // expect: true
+System.print(Foo.type.type.type.type.type == Class) // expect: true

test/core/fiber/abort.wren

@@ -2,6 +2,6 @@ var fiber = Fiber.new {
   Fiber.abort("Error message.")
 }
 
-IO.print(fiber.try()) // expect: Error message.
-IO.print(fiber.isDone) // expect: true
-IO.print(fiber.error) // expect: Error message.
+System.print(fiber.try()) // expect: Error message.
+System.print(fiber.isDone) // expect: true
+System.print(fiber.error) // expect: Error message.

test/core/fiber/call.wren

@@ -1,7 +1,7 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
 }
 
-IO.print("before") // expect: before
+System.print("before") // expect: before
 fiber.call()       // expect: fiber
-IO.print("after")  // expect: after
+System.print("after")  // expect: after

test/core/fiber/call_done.wren

@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("call")
+  System.print("call")
 }
 
 fiber.call() // expect: call

test/core/fiber/call_error.wren

@@ -1,6 +1,6 @@
 var fiber = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 fiber.try()

test/core/fiber/call_return_implicit_null.wren

@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("fiber") // expect: fiber
+  System.print("fiber") // expect: fiber
 }
 
-IO.print(fiber.call()) // expect: null
+System.print(fiber.call()) // expect: null

test/core/fiber/call_return_value.wren

@@ -1,6 +1,6 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
   return "result" // expect: fiber
 }
 
-IO.print(fiber.call()) // expect: result
+System.print(fiber.call()) // expect: result

test/core/fiber/call_transferred.wren

@@ -1,12 +1,12 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("transferred")
-  IO.print(main.transfer())
-  IO.print("called")
+  System.print("transferred")
+  System.print(main.transfer())
+  System.print("called")
 }
 
 fiber.transfer() // expect: transferred
-IO.print("main") // expect: main
+System.print("main") // expect: main
 fiber.call()     // expect: null
                  // expect: called

test/core/fiber/call_with_value.wren

@@ -1,9 +1,9 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
 }
 
 // The first value passed to the fiber is ignored, since there's no yield call
 // to return it.
-IO.print("before")    // expect: before
+System.print("before")    // expect: before
 fiber.call("ignored") // expect: fiber
-IO.print("after")     // expect: after
+System.print("after")     // expect: after

test/core/fiber/call_with_value_done.wren

@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("call")
+  System.print("call")
 }
 
 fiber.call(1) // expect: call

test/core/fiber/call_with_value_error.wren

@@ -1,6 +1,6 @@
 var fiber = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 fiber.try()

test/core/fiber/call_with_value_transferred.wren

@@ -1,12 +1,12 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("transferred")
-  IO.print(main.transfer())
-  IO.print("called")
+  System.print("transferred")
+  System.print(main.transfer())
+  System.print("called")
 }
 
 fiber.transfer()    // expect: transferred
-IO.print("main")    // expect: main
+System.print("main")    // expect: main
 fiber.call("value") // expect: value
                     // expect: called

test/core/fiber/error.wren

@@ -2,6 +2,6 @@ var fiber = Fiber.new {
   "s".unknown
 }
 
-IO.print(fiber.error) // expect: null
-IO.print(fiber.try()) // expect: String does not implement 'unknown'.
-IO.print(fiber.error) // expect: String does not implement 'unknown'.
+System.print(fiber.error) // expect: null
+System.print(fiber.try()) // expect: String does not implement 'unknown'.
+System.print(fiber.error) // expect: String does not implement 'unknown'.

test/core/fiber/is_done.wren

@@ -1,11 +1,11 @@
 var fiber = Fiber.new {
-  IO.print("1")
+  System.print("1")
   Fiber.yield()
-  IO.print("2")
+  System.print("2")
 }
 
-IO.print(fiber.isDone)  // expect: false
+System.print(fiber.isDone)  // expect: false
 fiber.call()            // expect: 1
-IO.print(fiber.isDone)  // expect: false
+System.print(fiber.isDone)  // expect: false
 fiber.call()            // expect: 2
-IO.print(fiber.isDone)  // expect: true
+System.print(fiber.isDone)  // expect: true

test/core/fiber/is_done_after_error.wren

@@ -3,4 +3,4 @@ var fiber = Fiber.new {
 }
 
 fiber.try()
-IO.print(fiber.isDone) // expect: true
+System.print(fiber.isDone) // expect: true

test/core/fiber/resume_caller.wren

@@ -1,16 +1,16 @@
 var b = Fiber.new {
-  IO.print("fiber b")
+  System.print("fiber b")
 }
 
 var a = Fiber.new {
-  IO.print("begin fiber a")
+  System.print("begin fiber a")
   b.call()
-  IO.print("end fiber a")
+  System.print("end fiber a")
 }
 
-IO.print("begin main")
+System.print("begin main")
 a.call()
-IO.print("end main")
+System.print("end main")
 
 // expect: begin main
 // expect: begin fiber a

test/core/fiber/transfer.wren

@@ -1,20 +1,20 @@
 var a = Fiber.new {
-  IO.print("a")
+  System.print("a")
 }
 
 var b = Fiber.new {
-  IO.print("b before")
+  System.print("b before")
   a.transfer()
-  IO.print("b after")
+  System.print("b after")
 }
 
 var c = Fiber.new {
-  IO.print("c before")
+  System.print("c before")
   b.transfer()
-  IO.print("c after")
+  System.print("c after")
 }
 
-IO.print("start") // expect: start
+System.print("start") // expect: start
 
 c.transfer()
 // expect: c before

test/core/fiber/transfer_direct_reenter.wren

@@ -1,9 +1,9 @@
 var F = Fiber.new {
-  IO.print(1)            // expect: 1
-  IO.print(F.transfer()) // expect: null
-  IO.print(2)            // expect: 2
+  System.print(1)            // expect: 1
+  System.print(F.transfer()) // expect: null
+  System.print(2)            // expect: 2
 }
 
 F.call()
 // F remembers its original caller so transfers back to main.
-IO.print(3) // expect: 3
+System.print(3) // expect: 3

test/core/fiber/transfer_indirect_reenter.wren

@@ -1,13 +1,13 @@
 var A = Fiber.new {
-  IO.print(2)
+  System.print(2)
   B.transfer()
-  IO.print("nope")
+  System.print("nope")
 }
 
 var B = Fiber.new {
-  IO.print(1)
+  System.print(1)
   A.transfer()
-  IO.print(3)
+  System.print(3)
 }
 
 B.call()
@@ -15,4 +15,4 @@ B.call()
 // expect: 2
 // expect: 3
 // B remembers its original caller so returns to main.
-IO.print(4) // expect: 4
+System.print(4) // expect: 4

test/core/fiber/transfer_return_call_value.wren

@@ -1,23 +1,23 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("fiber 1")
-  IO.print(main.transfer())
+  System.print("fiber 1")
+  System.print(main.transfer())
 
   // Yield to bounce back to main and clear the caller so we don't get a
   // double call() error below.
   Fiber.yield()
 
-  IO.print(main.transfer())
+  System.print(main.transfer())
 }
 
 fiber.transfer() // expect: fiber 1
-IO.print("main 1") // expect: main 1
+System.print("main 1") // expect: main 1
 fiber.call("call 1") // expect: call 1
 
-IO.print("main 2") // expect: main 2
+System.print("main 2") // expect: main 2
 // Transfer back into the fiber so it has a NULL caller.
 fiber.transfer()
 
 fiber.call() // expect: null
-IO.print("main 3") // expect: main 3
+System.print("main 3") // expect: main 3

test/core/fiber/transfer_return_transfer_value.wren

@@ -1,13 +1,13 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("fiber")
-  IO.print(main.transfer())
+  System.print("fiber")
+  System.print(main.transfer())
 }
 
 fiber.transfer() // expect: fiber
-IO.print("main") // expect: main
+System.print("main") // expect: main
 fiber.transfer("transfer") // expect: transfer
 
 // This does not get run since we exit when the transferred fiber completes.
-IO.print("nope")
+System.print("nope")

test/core/fiber/transfer_to_done.wren

@@ -1,5 +1,5 @@
 var a = Fiber.new {
-  IO.print("run")
+  System.print("run")
 }
 
 a.call() // expect: run

test/core/fiber/transfer_to_error.wren

@@ -1,6 +1,6 @@
 var a = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 a.try()

test/core/fiber/transfer_to_yielded.wren

@@ -1,7 +1,7 @@
 var fiber = Fiber.new {
-  IO.print("called")
-  IO.print(Fiber.yield())
-  IO.print("transferred")
+  System.print("called")
+  System.print(Fiber.yield())
+  System.print("transferred")
 }
 
 fiber.call()     // expect: called

test/core/fiber/transfer_with_value.wren

@@ -1,20 +1,20 @@
 var a = Fiber.new {
-  IO.print("a")
+  System.print("a")
 }
 
 var b = Fiber.new {
-  IO.print("b before")
+  System.print("b before")
   a.transfer("ignored")
-  IO.print("b after")
+  System.print("b after")
 }
 
 var c = Fiber.new {
-  IO.print("c before")
+  System.print("c before")
   b.transfer("ignored")
-  IO.print("c after")
+  System.print("c after")
 }
 
-IO.print("start") // expect: start
+System.print("start") // expect: start
 
 c.transfer("ignored")
 // expect: c before

test/core/fiber/transfer_with_value_direct_reenter.wren

@@ -1,8 +1,8 @@
 var F = Fiber.new {
-  IO.print(1) // expect: 1
-  IO.print(F.transfer("value")) // expect: value
-  IO.print(2) // expect: 2
+  System.print(1) // expect: 1
+  System.print(F.transfer("value")) // expect: value
+  System.print(2) // expect: 2
 }
 
 F.call()
-IO.print(3) // expect: 3
+System.print(3) // expect: 3

test/core/fiber/transfer_with_value_indirect_reenter.wren

@@ -1,17 +1,17 @@
 var A = Fiber.new {
-  IO.print(2)
+  System.print(2)
   B.transfer("ignored")
-  IO.print("nope")
+  System.print("nope")
 }
 
 var B = Fiber.new {
-  IO.print(1)
+  System.print(1)
   A.transfer("ignored")
-  IO.print(3)
+  System.print(3)
 }
 
 B.call()
 // expect: 1
 // expect: 2
 // expect: 3
-IO.print(4) // expect: 4
+System.print(4) // expect: 4

test/core/fiber/transfer_with_value_to_done.wren

@@ -1,5 +1,5 @@
 var a = Fiber.new {
-  IO.print("run")
+  System.print("run")
 }
 
 a.call() // expect: run

test/core/fiber/transfer_with_value_to_error.wren

@@ -1,6 +1,6 @@
 var a = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 a.try()

test/core/fiber/transfer_with_value_to_yielded.wren

@@ -1,7 +1,7 @@
 var fiber = Fiber.new {
-  IO.print("called")
-  IO.print(Fiber.yield())
-  IO.print("transferred")
+  System.print("called")
+  System.print(Fiber.yield())
+  System.print("transferred")
 }
 
 fiber.call()            // expect: called

test/core/fiber/try.wren

@@ -1,10 +1,10 @@
 var fiber = Fiber.new {
-  IO.print("before")
+  System.print("before")
   true.unknownMethod
-  IO.print("after")
+  System.print("after")
 }
 
-IO.print(fiber.try())
+System.print(fiber.try())
 // expect: before
 // expect: Bool does not implement 'unknownMethod'.
-IO.print("after try") // expect: after try
+System.print("after try") // expect: after try

test/core/fiber/try_when_done.wren

@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("try")
+  System.print("try")
 }
 
 fiber.try() // expect: try

test/core/fiber/try_without_error.wren

@@ -1,8 +1,8 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
 }
 
-IO.print("before")    // expect: before
-IO.print(fiber.try()) // expect: fiber
+System.print("before")    // expect: before
+System.print(fiber.try()) // expect: fiber
                       // expect: null
-IO.print("after")     // expect: after
+System.print("after")     // expect: after

test/core/fiber/type.wren

@@ -1,5 +1,5 @@
 var fiber = Fiber.new {}
-IO.print(fiber is Fiber)      // expect: true
-IO.print(fiber is Object)     // expect: true
-IO.print(fiber is Bool)       // expect: false
-IO.print(fiber.type == Fiber) // expect: true
+System.print(fiber is Fiber)      // expect: true
+System.print(fiber is Object)     // expect: true
+System.print(fiber is Bool)       // expect: false
+System.print(fiber.type == Fiber) // expect: true

test/core/fiber/yield.wren

@@ -1,14 +1,14 @@
 var fiber = Fiber.new {
-  IO.print("fiber 1")
+  System.print("fiber 1")
   Fiber.yield()
-  IO.print("fiber 2")
+  System.print("fiber 2")
   Fiber.yield()
-  IO.print("fiber 3")
+  System.print("fiber 3")
 }
 
 fiber.call()          // expect: fiber 1
-IO.print("main 1")    // expect: main 1
+System.print("main 1")    // expect: main 1
 fiber.call()          // expect: fiber 2
-IO.print("main 2")    // expect: main 2
+System.print("main 2")    // expect: main 2
 fiber.call()          // expect: fiber 3
-IO.print("main 3")    // expect: main 3
+System.print("main 3")    // expect: main 3

test/core/fiber/yield_from_main.wren

@@ -1,3 +1,3 @@
-IO.print("before") // expect: before
+System.print("before") // expect: before
 Fiber.yield()
-IO.print("not reached")
+System.print("not reached")

test/core/fiber/yield_return_call_value.wren

@@ -1,12 +1,12 @@
 var fiber = Fiber.new {
-  IO.print("fiber 1")
-  IO.print(Fiber.yield())
-  IO.print(Fiber.yield())
+  System.print("fiber 1")
+  System.print(Fiber.yield())
+  System.print(Fiber.yield())
 }
 
 fiber.call() // expect: fiber 1
-IO.print("main 1") // expect: main 1
+System.print("main 1") // expect: main 1
 fiber.call("call 1") // expect: call 1
-IO.print("main 2") // expect: main 2
+System.print("main 2") // expect: main 2
 fiber.call() // expect: null
-IO.print("main 3") // expect: main 3
+System.print("main 3") // expect: main 3

test/core/fiber/yield_return_transfer_value.wren

@@ -1,13 +1,13 @@
 var main = Fiber.current
 
 var a = Fiber.new {
-  IO.print("a")
-  IO.print(Fiber.yield())
+  System.print("a")
+  System.print(Fiber.yield())
 }
 
 var b = Fiber.new {
-  IO.print("b")
-  IO.print(Fiber.yield())
+  System.print("b")
+  System.print(Fiber.yield())
 
   a.call()
   a.transfer("value")

test/core/fiber/yield_with_no_caller.wren

@@ -1,7 +1,7 @@
 var a = Fiber.new {
-  IO.print("before") // expect: before
+  System.print("before") // expect: before
   Fiber.yield()
-  IO.print("not reached")
+  System.print("not reached")
 }
 
 // Transfer through a chain of fibers. Since none of them are called, they all
@@ -9,4 +9,4 @@ var a = Fiber.new {
 var b = Fiber.new { a.transfer() }
 var c = Fiber.new { b.transfer() }
 c.transfer()
-IO.print("not reached")
+System.print("not reached")

test/core/fiber/yield_with_value.wren

@@ -1,14 +1,14 @@
 var fiber = Fiber.new {
-  IO.print("fiber 1")
+  System.print("fiber 1")
   Fiber.yield("yield 1")
-  IO.print("fiber 2")
+  System.print("fiber 2")
   Fiber.yield("yield 2")
-  IO.print("fiber 3")
+  System.print("fiber 3")
 }
 
-IO.print(fiber.call())  // expect: fiber 1
+System.print(fiber.call())  // expect: fiber 1
                         // expect: yield 1
-IO.print(fiber.call())  // expect: fiber 2
+System.print(fiber.call())  // expect: fiber 2
                         // expect: yield 2
-IO.print(fiber.call())  // expect: fiber 3
+System.print(fiber.call())  // expect: fiber 3
                         // expect: null

test/core/fiber/yield_with_value_from_main.wren

@@ -1,3 +1,3 @@
-IO.print("before") // expect: before
+System.print("before") // expect: before
 Fiber.yield(1)
-IO.print("not reached")
+System.print("not reached")

test/core/fiber/yield_with_value_with_no_caller.wren

@@ -1,7 +1,7 @@
 var a = Fiber.new {
-  IO.print("before") // expect: before
+  System.print("before") // expect: before
   Fiber.yield(1)
-  IO.print("not reached")
+  System.print("not reached")
 }
 
 // Transfer through a chain of fibers. Since none of them are called, they all
@@ -9,4 +9,4 @@ var a = Fiber.new {
 var b = Fiber.new { a.transfer() }
 var c = Fiber.new { b.transfer() }
 c.transfer()
-IO.print("not reached")
+System.print("not reached")

test/core/function/arity.wren

@@ -1,5 +1,5 @@
-IO.print(Fn.new {}.arity) // expect: 0
-IO.print(Fn.new {|a| a}.arity) // expect: 1
-IO.print(Fn.new {|a, b| a}.arity) // expect: 2
-IO.print(Fn.new {|a, b, c| a}.arity) // expect: 3
-IO.print(Fn.new {|a, b, c, d| a}.arity) // expect: 4
+System.print(Fn.new {}.arity) // expect: 0
+System.print(Fn.new {|a| a}.arity) // expect: 1
+System.print(Fn.new {|a, b| a}.arity) // expect: 2
+System.print(Fn.new {|a, b, c| a}.arity) // expect: 3
+System.print(Fn.new {|a, b, c, d| a}.arity) // expect: 4

test/core/function/call_extra_arguments.wren

@@ -1,7 +1,7 @@
-var f0 = Fn.new { IO.print("zero") }
-var f1 = Fn.new {|a| IO.print("one ", a) }
-var f2 = Fn.new {|a, b| IO.print("two ", a, " ", b) }
-var f3 = Fn.new {|a, b, c| IO.print("three ", a, " ", b, " ", c) }
+var f0 = Fn.new { System.print("zero") }
+var f1 = Fn.new {|a| System.print("one " + a) }
+var f2 = Fn.new {|a, b| System.print("two " + a + " " + b) }
+var f3 = Fn.new {|a, b, c| System.print("three " + a + " " + b + " " + c) }
 
 f0.call("a") // expect: zero
 f0.call("a", "b") // expect: zero

test/core/function/call_missing_arguments.wren

@@ -1,2 +1,2 @@
-var f2 = Fn.new {|a, b| IO.print(a, b) }
+var f2 = Fn.new {|a, b| System.print(a, b) }
 f2.call("a") // expect runtime error: Function expects more arguments.

test/core/function/equality.wren

@@ -1,16 +1,16 @@
 // Not structurally equal.
-IO.print(Fn.new { 123 } == Fn.new { 123 })  // expect: false
-IO.print(Fn.new { 123 } != Fn.new { 123 })  // expect: true
+System.print(Fn.new { 123 } == Fn.new { 123 })  // expect: false
+System.print(Fn.new { 123 } != Fn.new { 123 })  // expect: true
 
 // Not equal to other types.
-IO.print(Fn.new { 123 } == 1)         // expect: false
-IO.print(Fn.new { 123 } == false)     // expect: false
-IO.print(Fn.new { 123 } == "fn 123")  // expect: false
-IO.print(Fn.new { 123 } != 1)         // expect: true
-IO.print(Fn.new { 123 } != false)     // expect: true
-IO.print(Fn.new { 123 } != "fn 123")  // expect: true
+System.print(Fn.new { 123 } == 1)         // expect: false
+System.print(Fn.new { 123 } == false)     // expect: false
+System.print(Fn.new { 123 } == "fn 123")  // expect: false
+System.print(Fn.new { 123 } != 1)         // expect: true
+System.print(Fn.new { 123 } != false)     // expect: true
+System.print(Fn.new { 123 } != "fn 123")  // expect: true
 
 // Equal by identity.
 var f = Fn.new { 123 }
-IO.print(f == f) // expect: true
-IO.print(f != f) // expect: false
+System.print(f == f) // expect: true
+System.print(f != f) // expect: false

test/core/function/to_string.wren

@@ -1 +1 @@
-IO.print(Fn.new {}) // expect: <fn>
+System.print(Fn.new {}) // expect: <fn>

test/core/function/type.wren

@@ -1,4 +1,4 @@
-IO.print(Fn.new { 0 } is Fn)      // expect: true
-IO.print(Fn.new { 0 } is Object)  // expect: true
-IO.print(Fn.new { 0 } is String)  // expect: false
-IO.print(Fn.new { 0 }.type == Fn) // expect: true
+System.print(Fn.new { 0 } is Fn)      // expect: true
+System.print(Fn.new { 0 } is Object)  // expect: true
+System.print(Fn.new { 0 } is String)  // expect: false
+System.print(Fn.new { 0 }.type == Fn) // expect: true

test/core/list/add.wren

@@ -1,8 +1,8 @@
 var a = [1]
 a.add(2)
-IO.print(a) // expect: [1, 2]
+System.print(a) // expect: [1, 2]
 a.add(3)
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
 
 // Returns added element.
-IO.print(a.add(4)) // expect: 4
+System.print(a.add(4)) // expect: 4

test/core/list/add_all.wren

@@ -1,11 +1,11 @@
 var a = [1]
 a.addAll([2, 3])
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
 a.addAll([])
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
 a.addAll(4..6)
-IO.print(a) // expect: [1, 2, 3, 4, 5, 6]
+System.print(a) // expect: [1, 2, 3, 4, 5, 6]
 
 // Returns argument.
 var range = 7..9
-IO.print(a.addAll(range) == range) // expect: true
+System.print(a.addAll(range) == range) // expect: true

test/core/list/clear.wren

@@ -1,7 +1,7 @@
 var a = [1, 2, 3]
 a.clear()
-IO.print(a)       // expect: []
-IO.print(a.count) // expect: 0
+System.print(a)       // expect: []
+System.print(a.count) // expect: 0
 
 // Returns null.
-IO.print([1, 2].clear()) // expect: null
+System.print([1, 2].clear()) // expect: null

test/core/list/contains.wren

@@ -1,6 +1,6 @@
 var list = [1, 2, 3, 4, "foo"]
 
-IO.print(list.contains(2))      // expect: true
-IO.print(list.contains(5))      // expect: false
-IO.print(list.contains("foo"))  // expect: true
-IO.print(list.contains("bar"))  // expect: false
+System.print(list.contains(2))      // expect: true
+System.print(list.contains(5))      // expect: false
+System.print(list.contains("foo"))  // expect: true
+System.print(list.contains("bar"))  // expect: false

test/core/list/count.wren

@@ -1,3 +1,3 @@
-IO.print([].count)           // expect: 0
-IO.print([1].count)          // expect: 1
-IO.print([1, 2, 3, 4].count) // expect: 4
+System.print([].count)           // expect: 0
+System.print([1].count)          // expect: 1
+System.print([1, 2, 3, 4].count) // expect: 4

test/core/list/count_predicate.wren

@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
 
-IO.print(a.count {|x| x > 3 })      // expect: 0
-IO.print(a.count {|x| x > 1 })      // expect: 2
+System.print(a.count {|x| x > 3 })      // expect: 0
+System.print(a.count {|x| x > 1 })      // expect: 2
 
-IO.print([].count {|x| true })      // expect: 0
+System.print([].count {|x| true })      // expect: 0

test/core/list/count_predicate_non_bool_returning_fn.wren

@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
 
-IO.print(a.count {|x| "truthy" })   // expect: 3
+System.print(a.count {|x| "truthy" })   // expect: 3

test/core/list/each.wren

@@ -1,3 +1,3 @@
 var words = ""
 ["One", "Two", "Three"].each {|word| words = words + word }
-IO.print(words) // expect: OneTwoThree
+System.print(words) // expect: OneTwoThree

test/core/list/each_no_items.wren

@@ -1,3 +1,3 @@
 var i = 0
 [].each {|item| i = i + 1 }
-IO.print(i) // expect: 0
+System.print(i) // expect: 0

test/core/list/insert.wren

@@ -1,41 +1,41 @@
 // Add to empty list.
 var a = []
 a.insert(0, 1)
-IO.print(a) // expect: [1]
+System.print(a) // expect: [1]
 
 // Normal indices.
 var b = [1, 2, 3]
 b.insert(0, 4)
-IO.print(b) // expect: [4, 1, 2, 3]
+System.print(b) // expect: [4, 1, 2, 3]
 
 var c = [1, 2, 3]
 c.insert(1, 4)
-IO.print(c) // expect: [1, 4, 2, 3]
+System.print(c) // expect: [1, 4, 2, 3]
 
 var d = [1, 2, 3]
 d.insert(2, 4)
-IO.print(d) // expect: [1, 2, 4, 3]
+System.print(d) // expect: [1, 2, 4, 3]
 
 var e = [1, 2, 3]
 e.insert(3, 4)
-IO.print(e) // expect: [1, 2, 3, 4]
+System.print(e) // expect: [1, 2, 3, 4]
 
 // Negative indices.
 var f = [1, 2, 3]
 f.insert(-4, 4)
-IO.print(f) // expect: [4, 1, 2, 3]
+System.print(f) // expect: [4, 1, 2, 3]
 
 var g = [1, 2, 3]
 g.insert(-3, 4)
-IO.print(g) // expect: [1, 4, 2, 3]
+System.print(g) // expect: [1, 4, 2, 3]
 
 var h = [1, 2, 3]
 h.insert(-2, 4)
-IO.print(h) // expect: [1, 2, 4, 3]
+System.print(h) // expect: [1, 2, 4, 3]
 
 var i = [1, 2, 3]
 i.insert(-1, 4)
-IO.print(i) // expect: [1, 2, 3, 4]
+System.print(i) // expect: [1, 2, 3, 4]
 
 // Returns.inserted value.
-IO.print([1, 2].insert(0, 3)) // expect: 3
+System.print([1, 2].insert(0, 3)) // expect: 3

test/core/list/iterate.wren

@@ -1,13 +1,13 @@
 var a = ["one", "two", "three", "four"]
-IO.print(a.iterate(null)) // expect: 0
-IO.print(a.iterate(0)) // expect: 1
-IO.print(a.iterate(1)) // expect: 2
-IO.print(a.iterate(2)) // expect: 3
-IO.print(a.iterate(3)) // expect: false
+System.print(a.iterate(null)) // expect: 0
+System.print(a.iterate(0)) // expect: 1
+System.print(a.iterate(1)) // expect: 2
+System.print(a.iterate(2)) // expect: 3
+System.print(a.iterate(3)) // expect: false
 
 // Out of bounds.
-IO.print(a.iterate(123)) // expect: false
-IO.print(a.iterate(-1)) // expect: false
+System.print(a.iterate(123)) // expect: false
+System.print(a.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty list.
-IO.print([].iterate(null)) // expect: false
+System.print([].iterate(null)) // expect: false

test/core/list/iterator_value.wren

@@ -1,5 +1,5 @@
 var a = ["one", "two", "three", "four"]
-IO.print(a.iteratorValue(0)) // expect: one
-IO.print(a.iteratorValue(1)) // expect: two
-IO.print(a.iteratorValue(2)) // expect: three
-IO.print(a.iteratorValue(3)) // expect: four
+System.print(a.iteratorValue(0)) // expect: one
+System.print(a.iteratorValue(1)) // expect: two
+System.print(a.iteratorValue(2)) // expect: three
+System.print(a.iteratorValue(3)) // expect: four

test/core/list/join.wren

@@ -1,17 +1,17 @@
 // Handle empty list.
-IO.print([].join(",") == "") // expect: true
+System.print([].join(",") == "") // expect: true
 
 // Handle a simple list with an empty delimeter.
-IO.print([1, 2, 3].join("")) // expect: 123
+System.print([1, 2, 3].join("")) // expect: 123
 
 // Handle a simple list with no separator.
-IO.print([1, 2, 3].join) // expect: 123
+System.print([1, 2, 3].join) // expect: 123
 
 // Does not quote strings.
-IO.print([1, "2", true].join(",")) // expect: 1,2,true
+System.print([1, "2", true].join(",")) // expect: 1,2,true
 
 // Nested lists.
-IO.print([1, [2, [3], 4], 5].join(",")) // expect: 1,[2, [3], 4],5
+System.print([1, [2, [3], 4], 5].join(",")) // expect: 1,[2, [3], 4],5
 
 // Calls toString on elements.
 class Foo {
@@ -19,6 +19,6 @@ class Foo {
   toString { "Foo.toString" }
 }
 
-IO.print([1, Foo.new(), 2].join(", ")) // expect: 1, Foo.toString, 2
+System.print([1, Foo.new(), 2].join(", ")) // expect: 1, Foo.toString, 2
 
 // TODO: Handle lists that contain themselves.

test/core/list/map.wren

@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
 var b = a.map {|x| x + 1 }.toList
-IO.print(b) // expect: [2, 3, 4]
+System.print(b) // expect: [2, 3, 4]

test/core/list/new.wren

@@ -1,6 +1,6 @@
 var list = List.new()
 
-IO.print(list.count) // expect: 0
-IO.print(list) // expect: []
+System.print(list.count) // expect: 0
+System.print(list) // expect: []
 list.add(1)
-IO.print(list) // expect: [1]
+System.print(list) // expect: [1]

test/core/list/not.wren

@@ -1,2 +1,2 @@
-IO.print(![1, 2]) // expect: false
-IO.print(![])     // expect: false
+System.print(![1, 2]) // expect: false
+System.print(![])     // expect: false

test/core/list/plus.wren

@@ -6,13 +6,13 @@ var e = a + []
 var f = [] + a
 var g = [] + []
 
-IO.print(a) // expect: [1, 2, 3]
-IO.print(b) // expect: [4, 5, 6]
-IO.print(c) // expect: [1, 2, 3, 4, 5, 6]
-IO.print(d) // expect: [1, 2, 3, 4, 5, 6]
-IO.print(e) // expect: [1, 2, 3]
-IO.print(f) // expect: [1, 2, 3]
-IO.print(g) // expect: []
+System.print(a) // expect: [1, 2, 3]
+System.print(b) // expect: [4, 5, 6]
+System.print(c) // expect: [1, 2, 3, 4, 5, 6]
+System.print(d) // expect: [1, 2, 3, 4, 5, 6]
+System.print(e) // expect: [1, 2, 3]
+System.print(f) // expect: [1, 2, 3]
+System.print(g) // expect: []
 
 // Doesn't modify original list.
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]

test/core/list/reduce.wren

@@ -3,12 +3,12 @@ var b = ["W", "o", "r", "l", "d"]
 var max = Fn.new {|a, b| a > b ? a : b }
 var sum = Fn.new {|a, b| a + b }
 
-IO.print(a.reduce(max)) // expect: 5
-IO.print(a.reduce(10, max)) // expect: 10
+System.print(a.reduce(max)) // expect: 5
+System.print(a.reduce(10, max)) // expect: 10
 
-IO.print(a.reduce(sum)) // expect: 13
-IO.print(a.reduce(-1, sum)) // expect: 12
+System.print(a.reduce(sum)) // expect: 13
+System.print(a.reduce(-1, sum)) // expect: 12
 
 // sum also concatenates strings
-IO.print(b.reduce("Hello ", sum)) // expect: Hello World
-IO.print(b.reduce(sum)) // expect: World
+System.print(b.reduce("Hello ", sum)) // expect: Hello World
+System.print(b.reduce(sum)) // expect: World

test/core/list/reduce_single_item.wren

@@ -1,2 +1,2 @@
-IO.print([1].reduce {|a, b| 42 }) // expect: 1
-IO.print([].reduce(1) {|a, b| 42 }) // expect: 1
+System.print([1].reduce {|a, b| 42 }) // expect: 1
+System.print([].reduce(1) {|a, b| 42 }) // expect: 1

test/core/list/remove_at.wren

@@ -1,27 +1,27 @@
 var a = [1, 2, 3]
 a.removeAt(0)
-IO.print(a) // expect: [2, 3]
+System.print(a) // expect: [2, 3]
 
 var b = [1, 2, 3]
 b.removeAt(1)
-IO.print(b) // expect: [1, 3]
+System.print(b) // expect: [1, 3]
 
 var c = [1, 2, 3]
 c.removeAt(2)
-IO.print(c) // expect: [1, 2]
+System.print(c) // expect: [1, 2]
 
 // Index backwards from end.
 var d = [1, 2, 3]
 d.removeAt(-3)
-IO.print(d) // expect: [2, 3]
+System.print(d) // expect: [2, 3]
 
 var e = [1, 2, 3]
 e.removeAt(-2)
-IO.print(e) // expect: [1, 3]
+System.print(e) // expect: [1, 3]
 
 var f = [1, 2, 3]
 f.removeAt(-1)
-IO.print(f) // expect: [1, 2]
+System.print(f) // expect: [1, 2]
 
 // Return the removed value.
-IO.print([3, 4, 5].removeAt(1)) // expect: 4
+System.print([3, 4, 5].removeAt(1)) // expect: 4

test/core/list/subscript.wren

@@ -1,12 +1,12 @@
 // Returns elements.
 var list = ["a", "b", "c", "d"]
-IO.print(list[0]) // expect: a
-IO.print(list[1]) // expect: b
-IO.print(list[2]) // expect: c
-IO.print(list[3]) // expect: d
+System.print(list[0]) // expect: a
+System.print(list[1]) // expect: b
+System.print(list[2]) // expect: c
+System.print(list[3]) // expect: d
 
 // Allows indexing backwards from the end.
-IO.print(list[-4]) // expect: a
-IO.print(list[-3]) // expect: b
-IO.print(list[-2]) // expect: c
-IO.print(list[-1]) // expect: d
+System.print(list[-4]) // expect: a
+System.print(list[-3]) // expect: b
+System.print(list[-2]) // expect: c
+System.print(list[-1]) // expect: d

test/core/list/subscript_range.wren

@@ -1,35 +1,35 @@
 // Returns lists.
 var list = ["a", "b", "c", "d", "e"]
-IO.print(list[0..0]) // expect: [a]
-IO.print(list[1...1]) // expect: []
-IO.print(list[1..2]) // expect: [b, c]
-IO.print(list[1...2]) // expect: [b]
-IO.print(list[2..4]) // expect: [c, d, e]
-IO.print(list[2...5]) // expect: [c, d, e]
+System.print(list[0..0]) // expect: [a]
+System.print(list[1...1]) // expect: []
+System.print(list[1..2]) // expect: [b, c]
+System.print(list[1...2]) // expect: [b]
+System.print(list[2..4]) // expect: [c, d, e]
+System.print(list[2...5]) // expect: [c, d, e]
 
 // A backwards range reverses.
-IO.print(list[3..1]) // expect: [d, c, b]
-IO.print(list[3...1]) // expect: [d, c]
-IO.print(list[3...3]) // expect: []
+System.print(list[3..1]) // expect: [d, c, b]
+System.print(list[3...1]) // expect: [d, c]
+System.print(list[3...3]) // expect: []
 
 // Negative ranges index from the end.
-IO.print(list[-5..-2]) // expect: [a, b, c, d]
-IO.print(list[-5...-2]) // expect: [a, b, c]
-IO.print(list[-3..-5]) // expect: [c, b, a]
-IO.print(list[-3...-6]) // expect: [c, b, a]
+System.print(list[-5..-2]) // expect: [a, b, c, d]
+System.print(list[-5...-2]) // expect: [a, b, c]
+System.print(list[-3..-5]) // expect: [c, b, a]
+System.print(list[-3...-6]) // expect: [c, b, a]
 
 // Half-negative ranges are treated like the negative value is fixed before
 // walking the range.
-IO.print(list[-5..3]) // expect: [a, b, c, d]
-IO.print(list[-3...5]) // expect: [c, d, e]
-IO.print(list[-2..1]) // expect: [d, c, b]
-IO.print(list[-2...0]) // expect: [d, c, b]
+System.print(list[-5..3]) // expect: [a, b, c, d]
+System.print(list[-3...5]) // expect: [c, d, e]
+System.print(list[-2..1]) // expect: [d, c, b]
+System.print(list[-2...0]) // expect: [d, c, b]
 
-IO.print(list[1..-2]) // expect: [b, c, d]
-IO.print(list[2...-1]) // expect: [c, d]
-IO.print(list[4..-5]) // expect: [e, d, c, b, a]
-IO.print(list[3...-6]) // expect: [d, c, b, a]
+System.print(list[1..-2]) // expect: [b, c, d]
+System.print(list[2...-1]) // expect: [c, d]
+System.print(list[4..-5]) // expect: [e, d, c, b, a]
+System.print(list[3...-6]) // expect: [d, c, b, a]
 
 // An empty range at zero is allowed on an empty list.
-IO.print([][0...0]) // expect: []
-IO.print([][0..-1]) // expect: []
+System.print([][0...0]) // expect: []
+System.print([][0..-1]) // expect: []

test/core/list/subscript_setter.wren

@@ -4,13 +4,13 @@
   list[0] = 5
   list[1] = 6
   list[2] = 7
-  IO.print(list) // expect: [5, 6, 7]
+  System.print(list) // expect: [5, 6, 7]
 }
 
 // Returns right-hand side.
 {
   var list = [1, 2, 3]
-  IO.print(list[1] = 5) // expect: 5
+  System.print(list[1] = 5) // expect: 5
 }
 
 // Negative indices.
@@ -19,5 +19,5 @@
   list[-1] = 5
   list[-2] = 6
   list[-3] = 7
-  IO.print(list) // expect: [7, 6, 5]
+  System.print(list) // expect: [7, 6, 5]
 }

test/core/list/to_string.wren

@@ -1,11 +1,11 @@
 // Handle empty list.
-IO.print([].toString)             // expect: []
+System.print([].toString)             // expect: []
 
 // Does not quote strings.
-IO.print([1, "2", true].toString) // expect: [1, 2, true]
+System.print([1, "2", true].toString) // expect: [1, 2, true]
 
 // Nested lists.
-IO.print([1, [2, [3], 4], 5]) // expect: [1, [2, [3], 4], 5]
+System.print([1, [2, [3], 4], 5]) // expect: [1, [2, [3], 4], 5]
 
 // Calls toString on elements.
 class Foo {
@@ -13,6 +13,6 @@ class Foo {
   toString { "Foo.toString" }
 }
 
-IO.print([1, Foo.new(), 2]) // expect: [1, Foo.toString, 2]
+System.print([1, Foo.new(), 2]) // expect: [1, Foo.toString, 2]
 
 // TODO: Handle lists that contain themselves.

test/core/list/type.wren

@@ -1,5 +1,5 @@
-IO.print([] is List)      // expect: true
-IO.print([] is Sequence)  // expect: true
-IO.print([] is Object)    // expect: true
-IO.print([] is Bool)      // expect: false
-IO.print([].type == List) // expect: true
+System.print([] is List)      // expect: true
+System.print([] is Sequence)  // expect: true
+System.print([] is Object)    // expect: true
+System.print([] is Bool)      // expect: false
+System.print([].type == List) // expect: true

test/core/list/where.wren

@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
 var b = a.where {|x| x > 1 }.toList
-IO.print(b) // expect: [2, 3]
+System.print(b) // expect: [2, 3]
 
 var c = a.where {|x| x > 10 }.toList
-IO.print(c) // expect: []
+System.print(c) // expect: []

test/core/map/churn.wren

@@ -8,4 +8,4 @@ for (i in 0...100) {
   if (i >= 10) map.remove(i - 10)
 }
 
-IO.print(map.count) // expect: 10
+System.print(map.count) // expect: 10

test/core/map/clear.wren

@@ -1,7 +1,7 @@
 var a = {1: 1, 2: 2, 3: 3}
 a.clear()
-IO.print(a)       // expect: {}
-IO.print(a.count) // expect: 0
+System.print(a)       // expect: {}
+System.print(a.count) // expect: 0
 
 // Returns null.
-IO.print({1: 2}.clear()) // expect: null
+System.print({1: 2}.clear()) // expect: null

test/core/map/contains_key.wren

@@ -4,8 +4,8 @@ var map = {
   "three": 3
 }
 
-IO.print(map.containsKey("one")) // expect: true
-IO.print(map.containsKey("two")) // expect: true
-IO.print(map.containsKey("three")) // expect: true
-IO.print(map.containsKey("four")) // expect: false
-IO.print(map.containsKey("five")) // expect: false
+System.print(map.containsKey("one")) // expect: true
+System.print(map.containsKey("two")) // expect: true
+System.print(map.containsKey("three")) // expect: true
+System.print(map.containsKey("four")) // expect: false
+System.print(map.containsKey("five")) // expect: false

test/core/map/count.wren

@@ -1,12 +1,12 @@
 var map = {}
-IO.print(map.count) // expect: 0
+System.print(map.count) // expect: 0
 map["one"] = "value"
-IO.print(map.count) // expect: 1
+System.print(map.count) // expect: 1
 map["two"] = "value"
-IO.print(map.count) // expect: 2
+System.print(map.count) // expect: 2
 map["three"] = "value"
-IO.print(map.count) // expect: 3
+System.print(map.count) // expect: 3
 
 // Adding existing key does not increase count.
 map["two"] = "new value"
-IO.print(map.count) // expect: 3
+System.print(map.count) // expect: 3

test/core/map/empty_string_key.wren

@@ -2,4 +2,4 @@ var map = {
   "": "empty string"
 }
 
-IO.print(map[""]) // expect: empty string
+System.print(map[""]) // expect: empty string

test/core/map/key_iterate.wren

@@ -4,23 +4,23 @@ var a = {"one": 1, "two": 2, "three": 3, "four": 4}.keys
 // entry table and the hashing process isn't specified. So we just validate
 // what we can assume about them.
 
-IO.print(a.iterate(null) is Num) // expect: true
-IO.print(a.iterate(null) >= 0) // expect: true
+System.print(a.iterate(null) is Num) // expect: true
+System.print(a.iterate(null) >= 0) // expect: true
 
-IO.print(a.iterate(0) is Num) // expect: true
-IO.print(a.iterate(0) > 0) // expect: true
-IO.print(a.iterate(1) is Num) // expect: true
-IO.print(a.iterate(1) > 0) // expect: true
-IO.print(a.iterate(2) is Num) // expect: true
-IO.print(a.iterate(2) > 0) // expect: true
-IO.print(a.iterate(3) is Num) // expect: true
-IO.print(a.iterate(3) > 0) // expect: true
+System.print(a.iterate(0) is Num) // expect: true
+System.print(a.iterate(0) > 0) // expect: true
+System.print(a.iterate(1) is Num) // expect: true
+System.print(a.iterate(1) > 0) // expect: true
+System.print(a.iterate(2) is Num) // expect: true
+System.print(a.iterate(2) > 0) // expect: true
+System.print(a.iterate(3) is Num) // expect: true
+System.print(a.iterate(3) > 0) // expect: true
 
 var previous = -1
 var iterator = a.iterate(null)
 while (iterator) {
-  IO.print(iterator > previous)
-  IO.print(iterator is Num)
+  System.print(iterator > previous)
+  System.print(iterator is Num)
   previous = iterator
   iterator = a.iterate(iterator)
 }
@@ -38,8 +38,8 @@ while (iterator) {
 // expect: true
 
 // Out of bounds.
-IO.print(a.iterate(16)) // expect: false
-IO.print(a.iterate(-1)) // expect: false
+System.print(a.iterate(16)) // expect: false
+System.print(a.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty map.
-IO.print({}.keys.iterate(null)) // expect: false
+System.print({}.keys.iterate(null)) // expect: false

test/core/map/key_types.wren

@@ -12,17 +12,17 @@ var map = {
   fiber: "fiber"
 }
 
-IO.print(map[null]) // expect: null value
-IO.print(map[true]) // expect: true value
-IO.print(map[false]) // expect: false value
-IO.print(map[0]) // expect: zero
-IO.print(map[1.2]) // expect: 1 point 2
-IO.print(map[List]) // expect: list class
-IO.print(map["null"]) // expect: string value
-IO.print(map[1..3]) // expect: 1 to 3
-IO.print(map[fiber]) // expect: fiber
+System.print(map[null]) // expect: null value
+System.print(map[true]) // expect: true value
+System.print(map[false]) // expect: false value
+System.print(map[0]) // expect: zero
+System.print(map[1.2]) // expect: 1 point 2
+System.print(map[List]) // expect: list class
+System.print(map["null"]) // expect: string value
+System.print(map[1..3]) // expect: 1 to 3
+System.print(map[fiber]) // expect: fiber
 
-IO.print(map.count) // expect: 9
+System.print(map.count) // expect: 9
 
 // Use the same keys (but sometimes different objects) to ensure keys have the
 // right equality semantics.
@@ -35,13 +35,13 @@ map[[].type] = "new list class"
 map["nu" + "ll"] = "new string value"
 map[(3 - 2)..(1 + 2)] = "new 1 to 3"
 
-IO.print(map[null]) // expect: new null value
-IO.print(map[true]) // expect: new true value
-IO.print(map[false]) // expect: new false value
-IO.print(map[0]) // expect: new zero
-IO.print(map[1.2]) // expect: new 1 point 2
-IO.print(map[List]) // expect: new list class
-IO.print(map["null"]) // expect: new string value
-IO.print(map[1..3]) // expect: new 1 to 3
+System.print(map[null]) // expect: new null value
+System.print(map[true]) // expect: new true value
+System.print(map[false]) // expect: new false value
+System.print(map[0]) // expect: new zero
+System.print(map[1.2]) // expect: new 1 point 2
+System.print(map[List]) // expect: new list class
+System.print(map["null"]) // expect: new string value
+System.print(map[1..3]) // expect: new 1 to 3
 
-IO.print(map.count) // expect: 9
+System.print(map.count) // expect: 9

test/core/map/new.wren

@@ -1,4 +1,4 @@
 var map = Map.new()
 
-IO.print(map.count) // expect: 0
-IO.print(map) // expect: {}
+System.print(map.count) // expect: 0
+System.print(map) // expect: {}

test/core/map/remove.wren

@@ -4,15 +4,15 @@ var map = {
   "three": 3
 }
 
-IO.print(map.count) // expect: 3
-IO.print(map.remove("two")) // expect: 2
-IO.print(map.count) // expect: 2
-IO.print(map.remove("three")) // expect: 3
-IO.print(map.count) // expect: 1
+System.print(map.count) // expect: 3
+System.print(map.remove("two")) // expect: 2
+System.print(map.count) // expect: 2
+System.print(map.remove("three")) // expect: 3
+System.print(map.count) // expect: 1
 
 // Remove an already removed entry.
-IO.print(map.remove("two")) // expect: null
-IO.print(map.count) // expect: 1
+System.print(map.remove("two")) // expect: null
+System.print(map.count) // expect: 1
 
-IO.print(map.remove("one")) // expect: 1
-IO.print(map.count) // expect: 0
+System.print(map.remove("one")) // expect: 1
+System.print(map.count) // expect: 0

test/core/map/subscript_empty_map.wren

@@ -1,4 +1,4 @@
 // This is a regression test to ensure map handles a null entry array.
 
 var map = {}
-IO.print(map["key"]) // expect: null
+System.print(map["key"]) // expect: null

test/core/map/to_string.wren

@@ -1,11 +1,11 @@
 // Handle empty map.
-IO.print({}.toString)             // expect: {}
+System.print({}.toString)             // expect: {}
 
 // Does not quote strings.
-IO.print({"1": "2"}.toString) // expect: {1: 2}
+System.print({"1": "2"}.toString) // expect: {1: 2}
 
 // Nested maps.
-IO.print({1: {2: {}}}) // expect: {1: {2: {}}}
+System.print({1: {2: {}}}) // expect: {1: {2: {}}}
 
 // Calls toString on elements.
 class Foo {
@@ -13,12 +13,12 @@ class Foo {
   toString { "Foo.toString" }
 }
 
-IO.print({1: Foo.new()}) // expect: {1: Foo.toString}
+System.print({1: Foo.new()}) // expect: {1: Foo.toString}
 
 // Since iteration order is unspecified, we don't know what order the results
 // will be.
 var s = {1: 2, 3: 4, 5: 6}.toString
-IO.print(s == "{1: 2, 3: 4, 5: 6}" ||
+System.print(s == "{1: 2, 3: 4, 5: 6}" ||
          s == "{1: 2, 5: 6, 3: 4}" ||
          s == "{3: 4, 1: 2, 5: 6}" ||
          s == "{3: 4, 5: 6, 1: 2}" ||

test/core/map/type.wren

@@ -1,5 +1,5 @@
-IO.print({} is Map)      // expect: true
+System.print({} is Map)      // expect: true
 // TODO: Abstract base class for associations.
-IO.print({} is Object)    // expect: true
-IO.print({} is Bool)      // expect: false
-IO.print({}.type == Map) // expect: true
+System.print({} is Object)    // expect: true
+System.print({} is Bool)      // expect: false
+System.print({}.type == Map) // expect: true

test/core/map/value_iterate.wren

@@ -4,23 +4,23 @@ var a = {"one": 1, "two": 2, "three": 3, "four": 4}.values
 // entry table and the hashing process isn't specified. So we just validate
 // what we can assume about them.
 
-IO.print(a.iterate(null) is Num) // expect: true
-IO.print(a.iterate(null) >= 0) // expect: true
+System.print(a.iterate(null) is Num) // expect: true
+System.print(a.iterate(null) >= 0) // expect: true
 
-IO.print(a.iterate(0) is Num) // expect: true
-IO.print(a.iterate(0) > 0) // expect: true
-IO.print(a.iterate(1) is Num) // expect: true
-IO.print(a.iterate(1) > 0) // expect: true
-IO.print(a.iterate(2) is Num) // expect: true
-IO.print(a.iterate(2) > 0) // expect: true
-IO.print(a.iterate(3) is Num) // expect: true
-IO.print(a.iterate(3) > 0) // expect: true
+System.print(a.iterate(0) is Num) // expect: true
+System.print(a.iterate(0) > 0) // expect: true
+System.print(a.iterate(1) is Num) // expect: true
+System.print(a.iterate(1) > 0) // expect: true
+System.print(a.iterate(2) is Num) // expect: true
+System.print(a.iterate(2) > 0) // expect: true
+System.print(a.iterate(3) is Num) // expect: true
+System.print(a.iterate(3) > 0) // expect: true
 
 var previous = -1
 var iterator = a.iterate(null)
 while (iterator) {
-  IO.print(iterator > previous)
-  IO.print(iterator is Num)
+  System.print(iterator > previous)
+  System.print(iterator is Num)
   previous = iterator
   iterator = a.iterate(iterator)
 }
@@ -38,8 +38,8 @@ while (iterator) {
 // expect: true
 
 // Out of bounds.
-IO.print(a.iterate(16)) // expect: false
-IO.print(a.iterate(-1)) // expect: false
+System.print(a.iterate(16)) // expect: false
+System.print(a.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty map.
-IO.print({}.values.iterate(null)) // expect: false
+System.print({}.values.iterate(null)) // expect: false

test/core/null/not.wren

@@ -1 +1 @@
-IO.print(!null) // expect: true
+System.print(!null) // expect: true

test/core/null/type.wren

@@ -1,4 +1,4 @@
-IO.print(null is Null)      // expect: true
-IO.print(null is Object)    // expect: true
-IO.print(null is Bool)      // expect: false
-IO.print(null.type == Null) // expect: true
+System.print(null is Null)      // expect: true
+System.print(null is Object)    // expect: true
+System.print(null is Bool)      // expect: false
+System.print(null.type == Null) // expect: true

test/core/number/abs.wren

@@ -1,6 +1,6 @@
-IO.print(123.abs)      // expect: 123
-IO.print((-123).abs)   // expect: 123
-IO.print(0.abs)        // expect: 0
-IO.print((-0).abs)     // expect: 0
-IO.print((-0.12).abs)  // expect: 0.12
-IO.print(12.34.abs)    // expect: 12.34
+System.print(123.abs)      // expect: 123
+System.print((-123).abs)   // expect: 123
+System.print(0.abs)        // expect: 0
+System.print((-0).abs)     // expect: 0
+System.print((-0.12).abs)  // expect: 0.12
+System.print(12.34.abs)    // expect: 12.34

test/core/number/acos.wren

@@ -1,3 +1,3 @@
-IO.print(0.acos)        // expect: 1.5707963267949
-IO.print(1.acos)        // expect: 0
-IO.print((-1).acos)     // expect: 3.1415926535898
+System.print(0.acos)        // expect: 1.5707963267949
+System.print(1.acos)        // expect: 0
+System.print((-1).acos)     // expect: 3.1415926535898

test/core/number/asin.wren

@@ -1,3 +1,3 @@
-IO.print(0.asin)        // expect: 0
-IO.print(1.asin)        // expect: 1.5707963267949
-IO.print((-1).asin)     // expect: -1.5707963267949
+System.print(0.asin)        // expect: 0
+System.print(1.asin)        // expect: 1.5707963267949
+System.print((-1).asin)     // expect: -1.5707963267949

test/core/number/atan.wren

@@ -1,2 +1,2 @@
-IO.print(0.atan)        // expect: 0
-IO.print(1.atan)        // expect: 0.78539816339745
+System.print(0.atan)        // expect: 0
+System.print(1.atan)        // expect: 0.78539816339745